Stimulus-permeability coupling in rat pulmonary macrophages challenged by Pseudomonas aeruginosa. An X-ray microanalysis study

Electron probe X-ray microanalysis (XRMA) of freeze-dried ultrathin sections provides the capability of measuring intracellular elemental content. This methodology was used to investigate the stimulus-permeability coupling responses associated with phagocytosis of Pseudomonas aeruginosa by cultured pulmonary alveolar macrophages (PAMs) of rats. PAMs were challenged with P. aeruginosa suspended in Gey's buffer at a bacteria to PAM ratio of 50:1 for 1 h at 37 degrees C. A 1-mm3 pellet of the unchallenged control PAMs, challenged PAMs and P. aeruginosa alone was quench-frozen in nitrogen-cooled, liquid propane, and 0.1-micron cryosections were cut at -100 degrees C. X-ray spectra were collected for nucleus and cytoplasm of 39 control PAMs, 36 challenged PAMs and 40 P. aeruginosa. Concentrations (mmole/kg dry weight) were obtained for Na, Cl, K, Ca, Mg, P, S for each cell. In the control PAMs, the content was similar to other mammalian cells. Moreover, there were no differences in elemental content between nucleus an cytoplasm. In the challenged PAMs, Na concentration was 4 times that of control PAMs (p less than 0.001) whereas Cl was double (p less than 0.001), K was 29% lower (p less than 0.001), and Ca was 4 times higher (p less than 0.05). The elemental concentration profile in the P. aeruginosa was distinctly different from that of the PAMs: higher Na, Ca, Mg, but lower Cl and K values. These results demonstrated elemental content changes in cultured PAMs challenged with P. aeruginosa that indicate a stimulus-permeability response by membranes associated with the phagocytic process.